Systems and methods herein generally relate to printing devices and methods that process images into pixels for printing purposes, and more particularly to methods and systems that control registration errors between different regions of an image.
Printing errors sometimes occur when different colors are not properly aligned on a sheet of media that can result in gaps between colors, which can cause undesirable white spaces or artifacts to appear on the printed image. Some solutions to such misregistration use a process known as trapping.
“Trapping” is a term which generically describes a hardware and/or software process used to compensate for the small amount that the paper tends to wander as it travels through a printing press. Trapping compensates for mechanical shifts or stretching of paper in the printing process and provides an overlap of colors to prevent unprinted paper from showing in the final printed product. Trapping helps preserve the integrity or the shape of an image. Without trapping unsightly gaps are likely to appear between two colors that are supposed to be touching. With trapping, one color is made to overlap the other by extending that color into a surrounding area. This allows the colors to keep touching one another, even as the paper wanders. In simple trapping, where two colors are involved, the submissive color is spread into the dominant color.
Another process used to compensate for color registration errors in printing which is referred to as “black over-print” is sometimes used. Black over-print changes the behavior of renderings, such as PostScript® (PS) renderings (PostScript® is a registered trademark of Adobe Systems, Inc., San Jose Calif.) so that the rendered content under solid black color is not cut out. The over-print method at the PS interpreter level is done for all the area under the solid black color. More elaborate trapping methods have been developed to handle color registration errors, but due to the complexity of the algorithms, they may not be suitable for system with limited processing resources in the image path. Also, even with sophisticated schemes for trapping condition detection and trapping pixel placement calculation, errors can still happen, which may lead to artifacts.